Mind Over Milkshake: How Your Thoughts Fool Your Stomach

It was late, almost 9 at night, when Justin Holden pulled the icy pizza box from the refrigerator at the Brookville Supermarket in Washington, D.C.

He stood in front of the open door, scanning the nutrition facts label.

A close relative had recently had a heart attack, and in the back of his mind there was this idea stalking him: If he put too much salt in his body, it would eventually kill him.

For this reason the information in the label wasn't exactly soothing: 1,110 milligrams of sodium seemed like a lot.

But there was even worse-sounding stuff at the bottom of the label.

Words like "diglyceride," with a string of letters that clearly had no business sitting next to each other. It suggested that something deeply unnatural was sitting inside the box.

"Obviously it's not good for me," the 20ish Holden said. "But, hopefully, I can let it slide in."

He tucked the pizza under his arm, and headed one aisle over for a sports drink.

A Label Is More Than A Label

Who among us has not had a moment like this? That intimate tete-a-tete with the nutrition label, searching out salt, sugar, fat, trying to discern: How will you affect me?Are you good? Or are you bad?

Here's the thing you probably haven't stopped to consider: how the label itself is affecting you.

"Labels are not just labels; they evoke a set of beliefs," says Alia Crum, a clinical psychologist who does research at the Columbia Business School in New York.

A couple of years ago, Crum found herself considering what seems like a pretty strange question. She wanted to know whether the information conveyed by a nutritional label could physically change what happens to you — "whether these labels get under the skin literally," she says, "and actually affect the body's physiological processing of the nutrients that are consumed."

Who among us has not had a moment like this? That intimate tete-a-tete with the nutrition label, searching out salt, sugar, fat, trying to discern: How will you affect me? Are you good? Or are you bad?

As a student, Crum had spent years studying the placebo effect — how a sugar pill can physically alter a body if the person taking the pill believes it will. She figured food labels might work the same way. So she came up with an experiment.

Crum created a huge batch of French vanilla milkshake, then divided it into two batches that were labeled in two very different ways.

Half the stuff was put into bottles labeled as a low-calorie drink called Sensishake — advertised as having zero percent fat, zero added sugar and only 140 calories.

The other half was put into bottles that were labeled as containing an incredibly rich treat called Indulgence. According to the label, Indulgence had all kinds of things that wouldn't benefit your upper thighs — including enough sugar and fat to account for 620 calories. In truth, the shakes had 300 calories each.

Both before and after the people in the study drank their shakes, nurses measured their levels of a hormone called ghrelin.

Ghrelin is a hormone secreted in the gut. People in the medical profession call it the hunger hormone. When ghrelin levels in the stomach rise, that signals the brain that it's time to seek out food.

"It also slows metabolism," Crum says, "just in case you might not find that food."

But after your ghrelin rises, and you have a big meal (say a cheeseburger and a side of fries), then your ghrelin levels drop. That signals the mind, Crum says, that "you've had enough here, and I'm going to start revving up the metabolism so we can burn the calories we've just ingested."

On the other hand, if you only have a small salad, your ghrelin levels don't drop that much, and metabolism doesn't get triggered in the same way.

For a long time scientists thought ghrelin levels fluctuated in response to nutrients that the ghrelin met in the stomach. So put in a big meal, ghrelin responds one way; put in a small snack and it responds another way.

If you believed you were drinking the indulgent shake, she says, your body responded as if you had consumed much more.

I don't think we've given enough credit to the role of our beliefs in determining our physiology, our reality.

- Alia Crum

"The ghrelin levels dropped about three times more when people were consuming the indulgent shake (or thought they were consuming the indulgent shake)," she says, compared to the people who drank the sensible shake (or thought that's what they were drinking).

Does that mean the facts don't matter, that it's what we think of the facts that matters?

"I don't think I would go that far yet," Crum says. More tests need to be done, she says, to figure out exactly how much influence comes from food and mindset.

But she does think the usual metabolic model — calories in and calories out — might need some rethinking, because it doesn't account in any way for our beliefs about our food.

"Our beliefs matter in virtually every domain, in everything we do," Crum says. "How much is a mystery, but I don't think we've given enough credit to the role of our beliefs in determining our physiology, our reality. We have this very simple metabolic science: calories in, calories out."

People don't want to think that our beliefs have influence, too, she says. "But they do!"

Meanwhile, Back At The Brookville Supermarket

As for Holden, after he retrieved his sports drink, he picked up a salad, then carried his items to the cashier and put them down on the conveyor belt.

The liquid of his sports drink almost glowed under the lights of the store as the cashier rang him up.

Holden told the man he didn't want a bag. He carried his pizza out into the night.

Within an hour, the pizza and drink would be in his stomach, mingling there with a set of beliefs that he got from the back of a box.

Shots is the online channel for health stories from the NPR Science Desk. We report on news that can make a difference for your health and show how policy shapes our health choices. Look to Shots for the latest on research and medical treatments, as well as the business side of health. Your hosts are Scott Hensley and Nancy Shute. You can reach the Shots team via our contact form.